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Item The Shadow Meets the Mask: Pyramid-Based Shadow Removal(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shor, Yael; Lischinski, DaniIn this paper we propose a novel method for detecting and removing shadows from a single image thereby obtaining a high-quality shadow-free image. With minimal user assistance, we first identify shadowed and lit areas on the same surface in the scene using an illumination-invariant distance measure. These areas are used to estimate the parameters of an affine shadow formation model. A novel pyramid-based restoration process is then applied to produce a shadow-free image, while avoiding loss of texture contrast and introduction of noise. Unlike previous approaches, we account for varying shadow intensity inside the shadowed region by processing it from the interior towards the boundaries. Finally, to ensure a seamless transition between the original and the recovered regions we apply image inpainting along a thin border. We demonstrate that our approach produces results that are in most cases superior in quality to those of previous shadow removal methods. We also show that it is possible to easily composite the extracted shadow onto a new background or modify its size and direction in the original image.Item Computer Graphics Curriculum: a Programming Approach(The Eurographics Association, 2008) Sobczyk, Dominique; Touzeau, Marie-Solange; Bourdin, Jean-Jacques; Steve Cunningham and Lars KjelldahlAt University Paris 8 the computer science curriculum is focused on programming as a good technique to improve the skills of students and to improve the success of studies. It has been reinforced when France adopted the Bologna requirements. This approach is well adapted to our computer graphics courses. The results of these courses are discussed.Item Crowds in Context: Evaluating the Perceptual Plausibility of Pedestrian Orientations(The Eurographics Association, 2008) Peters, Christopher; Ennis, Cathy; McDonnell, Rachel; O'Sullivan, Carol; Katerina Mania and Eric ReinhardWe describe a work-in-progress evaluating the plausibility of pedestrian orientations. While many studies have focused on creating accurate or fast crowd simulation models for populating virtual cities or other environments, little is known about how humans perceive the characteristics of generated scenes. Our initial study, reported here, consists of an evaluation based on static imagery reconstructed from annotated photographs, where the orientations of individuals have been modified. An important focus in our research is the consideration of the effects of the context of the scene on the evaluation, in terms of nearby individuals, objects and the constraints of the walking zone. This work could prove significant for improving and informing the creation of computer graphics pedestrian models. Our particular aim is to inform level-of-detail modelsItem Graphics based Computer Adaptive Testing and Beyond(The Eurographics Association, 2008) Cheng, Irene; Basu, Anup; Steve Cunningham and Lars KjelldahlInstead of computer games, animations, cartoons, and videos being used only for entertainment by kids, there is now an interest in using graphics for 'innovative testing'. Rather than traditional pen-and-paper tests, audio, video and graphics are being conceived as alternative means for more effective testing in the future. In this paper we review some examples of graphics item types for testing. As well, we outline how games can be used to interactively test concepts; discuss designing chemistry item types with interactive graphics; suggest approaches for automatically adjusting difficulty level in interactive graphics based questions; and propose strategies for giving partial marks for incorrect answers. We study how to test different cognitive skills, such as music, using multimedia interfaces; and also evaluate the effectiveness of our model. A method for estimating difficulty level of a mathematical item type using Item Response Theory (IRT) is discussed. Evaluation of the graphics item types through extensive testing on some students is also described. All of the graphics implementations shown in this report are developed by members of our research group.Item Adaptive Remeshing of Non-Manifold Surfaces(The Eurographics Association, 2008) Zilske, Michael; Lamecker, Hans; Zachow, Stefan; Katerina Mania and Eric ReinhardWe present a unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines, which together form a feature skeleton. Our method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature skeleton and the input mesh.Item Interactive Volume Rendering with Dynamic Ambient Occlusion and Color Bleeding(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ropinski, Timo; Meyer-Spradow, Jennis; Diepenbrock, Stefan; Mensmann, Joerg; Hinrichs, KlausWe propose a method for rendering volumetric data sets at interactive frame rates while supporting dynamic ambient occlusion as well as an approximation to color bleeding. In contrast to ambient occlusion approaches for polygonal data, techniques for volumetric data sets have to face additional challenges, since by changing rendering parameters, such as the transfer function or the thresholding, the structure of the data set and thus the light interactions may vary drastically. Therefore, during a preprocessing step which is independent of the rendering parameters we capture light interactions for all combinations of structures extractable from a volumetric data set. In order to compute the light interactions between the different structures, we combine this preprocessed information during rendering based on the rendering parameters defined interactively by the user. Thus our method supports interactive exploration of a volumetric data set but still gives the user control over the most important rendering parameters. For instance, if the user alters the transfer function to extract different structures from a volumetric data set the light interactions between the extracted structures are captured in the rendering while still allowing interactive frame rates. Compared to known local illumination models for volume rendering our method does not introduce any substantial rendering overhead and can be integrated easily into existing volume rendering applications. In this paper we will explain our approach, discuss the implications for interactive volume rendering and present the achieved results.Item GPU Accelerated Direct Volume Rendering on an Interactive Light Field Display(The Eurographics Association and Blackwell Publishing Ltd, 2008) Agus, Marco; Gobbetti, Enrico; Guitian, Jose Antonio Iglesias; Marton, Fabio; Pintore, GiovanniWe present a GPU accelerated volume ray casting system interactively driving a multi-user light field display. The display, driven by a single programmable GPU, is based on a specially arranged array of projectors and a holographic screen and provides full horizontal parallax. The characteristics of the display are exploited to develop a specialized volume rendering technique able to provide multiple freely moving naked-eye viewers the illusion of seeing and manipulating virtual volumetric objects floating in the display workspace. In our approach, a GPU ray-caster follows rays generated by a multiple-center-of-projection technique while sampling pre-filtered versions of the dataset at resolutions that match the varying spatial accuracy of the display. The method achieves interactive performance and provides rapid visual understanding of complex volumetric data sets even when using depth oblivious compositing techniques.Item Reduced Depth and Visual Hulls of Complex 3D Scenes(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bogomjakov, Alexander; Gotsman, CraigDepth and visual hulls are useful for quick reconstruction and rendering of a 3D object based on a number of reference views. However, for many scenes, especially multi-object, these hulls may contain significant artifacts known as phantom geometry. In depth hulls the phantom geometry appears behind the scene objects in regions occluded from all the reference views. In visual hulls the phantom geometry may also appear in front of the objects because there is not enough information to unambiguously imply the object positions.In this work we identify which parts of the depth and visual hull might constitute phantom geometry. We define the notion of reduced depth hull and reduced visual hull as the parts of the corresponding hull that are phantom-free. We analyze the role of the depth information in identification of the phantom geometry. Based on this, we provide an algorithm for rendering the reduced depth hull at interactive frame-rates and suggest an approach for rendering the reduced visual hull. The rendering algorithms take advantage of modern GPU programming techniques.Our techniques bypass explicit reconstruction of the hulls, rendering the reduced depth or visual hull directly from the reference views.Item Higher Order Barycentric Coordinates(The Eurographics Association and Blackwell Publishing Ltd, 2008) Langer, Torsten; Seidel, Hans-PeterIn recent years, a wide range of generalized barycentric coordinates has been suggested. However, all of them lack control over derivatives. We show how the notion of barycentric coordinates can be extended to specify derivatives at control points. This is also known as Hermite interpolation. We introduce a method to modify existing barycentric coordinates to higher order barycentric coordinates and demonstrate, using higher order mean value coordinates, that our method, although conceptually simple and easy to implement, can be used to give easy and intuitive control at interactive frame rates over local space deformations such as rotations.Item Automatic Conversion of Mesh Animations into Skeleton-based Animations(The Eurographics Association and Blackwell Publishing Ltd, 2008) De Aguiar, Edilson; Theobalt, Christian; Thrun, Sebastian; Seidel, Hans-PeterRecently, it has become increasingly popular to represent animations not by means of a classical skeleton-based model, but in the form of deforming mesh sequences. The reason for this new trend is that novel mesh deformation methods as well as new surface based scene capture techniques offer a great level of flexibility during animation creation. Unfortunately, the resulting scene representation is less compact than skeletal ones and there is not yet a rich toolbox available which enables easy post-processing and modification of mesh animations. To bridge this gap between the mesh-based and the skeletal paradigm, we propose a new method that automatically extracts a plausible kinematic skeleton, skeletal motion parameters, as well as surface skinning weights from arbitrary mesh animations. By this means, deforming mesh sequences can be fully-automatically transformed into fullyrigged virtual subjects. The original input can then be quickly rendered based on the new compact bone and skin representation, and it can be easily modified using the full repertoire of already existing animation tools.Item Render2MPEG: A Perception-based Framework Towards Integrating Rendering and Video Compression(The Eurographics Association and Blackwell Publishing Ltd, 2008) Herzog, Robert; Kinuwaki, Shinichi; Myszkowski, Karol; Seidel, Hans-PeterCurrently 3D animation rendering and video compression are completely independent processes even if rendered frames are streamed on-the-fly within a client-server platform. In such scenario, which may involve time-varying transmission bandwidths and different display characteristics at the client side, dynamic adjustment of the rendering quality to such requirements can lead to a better use of server resources. In this work, we present a framework where the renderer and MPEG codec are coupled through a straightforward interface that provides precise motion vectors from the rendering side to the codec and perceptual error thresholds for each pixel in the opposite direction. The perceptual error thresholds take into account bandwidth-dependent quantization errors resulting from the lossy com-pression as well as image content-dependent luminance and spatial contrast masking. The availability of the discrete cosine transform (DCT) coefficients at the codec side enables to use advanced models of the human visual system (HVS) in the perceptual error threshold derivation without incurring any significant cost. Those error thresholds are then used to control the rendering quality and make it well aligned with the compressed stream quality. In our prototype system we use the lightcuts technique developed by Walter et al., which we enhance to handle dynamic image sequences, and an MPEG-2 implementation. Our results clearly demonstrate many advantages of coupling the rendering with video compression in terms of faster rendering. Furthermore, temporally coherent rendering leads to a reduction of temporal artifacts.Item Advanced Material Appearance Models(The Eurographics Association, 2008) Dorsey, Julie; Rushmeier, Holly; Sillion, Francois; Maria Roussou and Jason LeighThis tutorial will cover the foundational elements of advanced material appearance models. For many years appearance models in computer graphics focused on general models for reflectance functions coupled with texture maps. However, over the past few years it has been recognized that even very common materials such as hair, skin, fabric, and rusting metal require more sophisticated models to appear realistic. In the tutorial we will begin by briefly reviewing basic reflectance models and the use of texture maps. We will then describe some common themes in advanced material models that include combining the effects of layers, groups of particles and or fibers. We will survey the detailed models necessary needed to model materials such as (but not limited to) skin (including pigmentation, pores, subsurface scattering), plants (including internal structure affecting scattering and characteristic shapes) and paints (including color flop and sparkle effects in automotive paints). In the next section of the tutorial we will treat the modeling of complex appearance due to aging and weathering processes. A general taxonomy of these effects will be presented, as well as methods to simulate and to capture these effects. The tutorial will close with a look at current trends in material modeling research.Item Level of Detail Flow Simulation(The Eurographics Association, 2008) Klar, Gergely; Katerina Mania and Eric ReinhardIn this paper we present a framework to simulate visually plausible large scale flow of fluids or smoke. To maintain real-time speed, we define the simulation over a coarse grid which is refined with a more detailed grid at places where fine details may emerge, like around moving obstacles. The detailed grids also act as fixed frames of reference to the surrounded obstacles to prevent the need for working with moving boundaries in the flow.Item Expressive Facial Gestures From Motion Capture Data(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ju, Eunjung; Lee, JeheeHuman facial gestures often exhibit such natural stochastic variations as how often the eyes blink, how often the eyebrows and the nose twitch, and how the head moves while speaking. The stochastic movements of facial features are key ingredients for generating convincing facial expressions. Although such small variations have been simulated using noise functions in many graphics applications, modulating noise functions to match natural variations induced from the affective states and the personality of characters is difficult and not intuitive. We present a technique for generating subtle expressive facial gestures (facial expressions and head motion) semi-automatically from motion capture data. Our approach is based on Markov random fields that are simulated in two levels. In the lower level, the coordinated movements of facial features are captured, parameterized, and transferred to synthetic faces using basis shapes. The upper level represents independent stochastic behavior of facial features. The experimental results show that our system generates expressive facial gestures synchronized with input speech.Item Efficient Spherical Harmonics Lighting with the Preetham Skylight Model(The Eurographics Association, 2008) Habel, Ralf; Mustata, Bogdan; Wimmer, Michael; Katerina Mania and Eric ReinhardWe present a fast and compact representation of a skylight model for spherical harmonics lighting, especially for outdoor scenes. This representation allows dynamically changing the sun position and weather conditions on a per frame basis. We chose the most used model in real-time graphics, the Preetham skylight model, because it can deliver both realistic colors and dynamic range and its extension into spherical harmonics can be used to realistically light a scene. We separate the parameters of the Preetham skylight model s spherical harmonics extension and perform a polynomial two-dimensional non-linear least squares fit for the principal parameters to achieve both negligible memory and computation costs. Additionally, we execute a domain specific Gibbs phenomena suppression to remove ringing artifacts.Item Dynamic Sampling and Rendering of Algebraic Point Set Surfaces(The Eurographics Association and Blackwell Publishing Ltd, 2008) Guennebaud, Gael; Germann, Marcel; Gross, MarkusAlgebraic Point Set Surfaces (APSS) define a smooth surface from a set of points using local moving least-squares (MLS) fitting of algebraic spheres. In this paper we first revisit the spherical fitting problem and provide a new, more generic solution that includes intuitive parameters for curvature control of the fitted spheres. As a second contribution we present a novel real-time rendering system of such surfaces using a dynamic up-sampling strategy combined with a conventional splatting algorithm for high quality rendering. Our approach also includes a new view dependent geometric error tailored to efficient and adaptive up-sampling of the surface. One of the key features of our system is its high degree of flexibility that enables us to achieve high performance even for highly dynamic data or complex models by exploiting temporal coherence at the primitive level. We also address the issue of efficient spatial search data structures with respect to construction, access and GPU friendliness. Finally, we present an efficient parallel GPU implementation of the algorithms and search structures.Item Sketch-Based Procedural Surface Modeling and Compositing Using Surface Trees(The Eurographics Association and Blackwell Publishing Ltd, 2008) Schmidt, Ryan; Singh, KaranWe present a system for creating and manipulating layered procedural surface editing operations, which is motivated by the limited support for iterative design in free-form modeling. A combination of sketch-based and traditional modeling tools are used to design soft displacements, sharp creases, extrusions along 3D paths, and topological holes and handles. Using local parameterizations, these edits are combined in a dynamic hierarchy, enabling procedural operations like linked copy-and-paste and drag-and-drop layer-based editing. Such dynamic, layered surface compositing is formalized as a Surface Tree, an analog of CSG trees which generalizes previous hierarchical surface modeling techniques. By anchoring tree nodes in the parameter space of lower layers, our surface tree implementation can better preserve the semantics of an edit as the underlying surface changes. Details of our implementation are described, including an efficient procedural mesh data structure.Item Computer Graphics: Problem Based Learning and Interactive Embodied Pedagogical Agents(The Eurographics Association, 2008) Seron, Francisco; Cerezo, Eva; Baldassarri, Sandra; Steve Cunningham and Lars KjelldahlThis paper focuses on the use of new tools in order to improve the learning of Computer Graphics, in particular of some aspects that have been detected as specially difficult by the students. Within this context, this paper explores the union of two areas: the educational strategy named Problem-Based Learning (PBL) and the use of interactive embodied pedagogical agents (IEPAs) for education and training tasks. By combining these ideas, we obtain an interactive learning environment created to improve student's learning capabilities. From the PBL point of view, the real problem proposed to the students consists in the development of their own viewing system. While for introducing IEPAs we've developed a powerful engine, called Maxine, that enables the management of 3D environments with special emphasis in the use of embodied animated agents. The engine, based on open source libraries, allows emotional and multimodal interaction with the user in real-time: via text, voice, images, animation (facial expression, lip-synch, body gestures) and the choice of the answers. By carefully orchestrating both ideas the students are encouraged to care more about their own progress, convey the enthusiasm in the learner for the subject matter and simply make learning more fun. Evaluations already done to the students show promising results.Item Preface and Table of Contents(The Eurographics Association, 2008) -; Theoharis Theoharis and Philip DutrePreface and Table of ContentsItem A Semi-Lagrangian CIP Fluid Solver without Dimensional Splitting(The Eurographics Association and Blackwell Publishing Ltd, 2008) Kim, Doyub; Song, Oh-young; Ko, Hyeong-SeokIn this paper, we propose a new constrained interpolation profile (CIP) method that is stable and accurate but requires less amount of computation compared to existing CIP-based solvers. CIP is a high-order fluid advection solver that can reproduce rich details of fluids. It has third-order accuracy but its computation is performed over a compact stencil. These advantageous features of CIP are, however, diluted by the following two shortcomings: (1) CIP contains a defect in the utilization of the grid data, which makes the method suitable only for simulations with a tight CFL restriction; and (2) CIP does not guarantee unconditional stability. There have been several attempts to fix these problems in CIP, but they have been only partially successful. The solutions that fixed both problems ended up introducing other undesirable features, namely increased computation time and/or reduced accuracy. This paper proposes a novel modification of the original CIP method that fixes all of the above problems without increasing the computational load or reducing the accuracy. Both quantitative and visual experiments were performed to test the performance of the new CIP in comparison to existing fluid solvers. The results show that the proposed method brings significant improvements in both accuracy and speed.